Disney (NYSE:DIS) surprised investors when it announced Disney+ now has 50 million global subscribers. It's been only five months since the service's official launch in the U.S., and it's been mere days since it came to Western Europe and India.

It's now even more evident that Disney's five-year outlook for the service to reach between 60 million to 90 million global subscribers was too conservative. With upcoming launches in Japan, Eastern Europe, and Latin America, Disney+ still has a lot of subscriber growth left.

Still, there are some important details for investors to take away from Disney's announcement, and there are reasons to believe Disney's future growth will slow considerably.

The Disney+ home screen displayed on a television

Image source: Disney.

Breaking down those 50 million subscribers

Disney told investors it had 28.6 million Disney+ subscribers, most of which were in the United States, at the start of February during its first-quarter earnings call. It also said that was an increase from the 26.5 million subscribers it had at the end of 2019. Disney has likely seen a continued increase in U.S. subscribers over the past couple of months as consumers stay at home to help prevent the spread of coronavirus.

In its more recent announcement, Disney said its launch in India added about 8 million subscribers. Disney's India launch relied on its existing subscriber base to Hotstar. Existing Hotstar subscribers were automatically upgraded to Disney+ Hotstar, and their billing will reflect the new prices when their existing contracts expire (which may not be for several months). It's unclear how many of those 8 million subscribers are actually new customers for Disney.

That leaves about 12 million subscribers in Western European countries. Disney launched in the U.K., Ireland, Italy, Switzerland, Spain, Germany, and Austria on March 24. It added France on April 7. The subscription prices in those countries are similar to Disney's U.S. pricing, and the subscription revenue is entirely incremental to Disney's top line.

More growth is still to come

The Western European countries in which Disney recently launched exhibit similar affinities for Disney's brands as the company's early launch markets. If Disney can maintain the same penetration rate as it did in its early markets, that suggests the company will add another 12 million or so subscribers in those markets by the end of June.

That would put it well over the low end of its 60 million to 90 million subscriber outlook for 2024.

Meanwhile, Disney will launch in Japan, where it also has a strong brand. In fact, Disney launched a streaming service called Disney Deluxe in the country last year, which includes the Disney, Pixar, Marvel, and Star Wars catalog for 700 yen (about $6.50) per month. It's possible Disney will simply upgrade those existing subscribers to Disney+, like it did with Hotstar subscribers in India.

Disney will also add several other European and Latin American countries before the year ends.

Investors can expect Disney to add millions more subscribers in those markets, pushing the company's total well within its 60 million to 90 million outlook, and perhaps even beyond that number.

Expect slower subscriber growth in the future

While Disney has now had several successful Disney+ launches, it'll face a big challenge going forward in retaining all of those new subscribers.

Disney's content library is relatively thin compared to other streaming video companies such as Netflix (NASDAQ:NFLX). And there's potential it'll see significant production delays if the fight to stop the spread of coronavirus is prolonged. Netflix has said it has enough content in its pipeline for a few months of shutting down productions, but even the global leader could face a serious drought in new debuts if production doesn't pick back up quickly.

Disney has several big series set to debut later this year -- two new Marvel series and season 2 of The Mandalorian. Those series are expected to draw in lots of new subscribers and keep existing subscribers engaged enough to keep them re-upping their subscriptions. Delays will cause increased subscriber retention challenges, especially as existing subscribers come off of their full-year commitments in November and December.

Disney has done an excellent job of attracting subscribers to Disney+. Now it has to prove it can keep them.